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Proteins…read more

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Amino Acids
· Proteins are made of amino acids.
· Amino acids are made of 5 elements CHONS (carbon, hydrogen, oxygen,
nitrogen, sulfur)
· All amino acids have the same general structure ­ a carboxyl group (COOH), and
an amino group (NH) attached to a carbon atom. The difference between different
amino acids is the variable group (R).
· The amino group is attached by a covalent bond to a central carbon atom called
the alpha carbon.
· The R group determines the specific properties of a given amino acid (there are
20 different R groups)
· Amino acids are amphoteric; they
have both acidic and basic properties
when they dissociate in water.
· The ability to donate or receive protons
causes amino acid solutions to behave as
buffers.…read more

Slide 3

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Peptide Bonds
· Amino acids are linked together by peptide bonds to form dipeptides and
· It is a condensation reaction, which means a molecule of water is released during
the reaction. a hydrolysis reaction
· The reverse of this reaction adds a molecule of water to break the peptide bond.
· Dipeptide (2 amino acids join together), Tripeptide (3 amino acids join together),
polypeptide (many amino acids join together).
· Proteins are made up of one or more polypeptides.
· Amino acid polymerisation to form polypeptides is part of protein synthesis. It
takes place in ribosomes.…read more

Slide 4

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Protein Structure
Proteins are polymers made up of amino acid monomers.
Primary Structure: Amino acid
· This is the sequence of amino acids in the polypeptide chain.
· For example in myoglobin or any other protein to carry out its specific function, it
must contain the correct amino acids arranged in a precise order.
· If only one amino acid is out of place its function may be disrupted. For example; in
haemoglobin (the main oxygen-carrying blood protein) a change in a single amino acid,
causes sickle-cell anaemia, a serious blood disorder.
Secondary Structure:
· The polypeptide chain doesn't remain flat and straight.
· Hydrogen bonds form between the amino acids in the chain. This makes it
automatically coil into an alpha () helix or fold into a beta () pleated sheet.
· Both the helix and the sheet are held together by many hydrogen bonds, which makes
them very stable and strong structures.
Tertiary Structure:
· This refers to the 3D shape of a polypeptide chain.
· The tertiary structure is held together by bonds between the R group of the amino
acids in the protein. ( more bonds form in the tertiary structure)
· The coiled and folded chain of amino acid is often coiled and folded further.…read more

Slide 5

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Proteins are classified into 2 main groups on the basis of their tertiary structure;
globular or fibrous.
· Globular proteins:
· They have polypeptide chains that are tightly folded to form a spherical shape.
· Many are folded so that their hydrophobic groups are on the inside of the
molecule, and the hydrophilic groups face outwards, making these proteins soluble
in water.
· The group includes enzymes, antibiotics and many hormones.
· There shape is maintained by various bonds including ionic bonds, hydrogen bonds,
disulfide bonds and hydrophobic interactions.
· Fibrous proteins:
· Consists of parallel polypeptide chains, cross-linked at intervals to form long
fibres or sheets.
· They are usually insoluble in water and physically tough.
· They include collagen (bone), silk and keratin (hair). Haem group Alpha chain
Quaternary Structure:
· Many proteins consist of more than one polypeptide chain
bonded together. The quaternary structure is the
arrangement of the of the different chains.
· For example; Haemoglobin is made of 4 polypeptide chains
2 distinct types (alpha and beta) and 4 non-protein haem
Beta chain…read more

Slide 6

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Protein Denaturing
· If the hydrogen bonds holding the protein in shape are broken, a process called
denaturing occurs.
· The covalent bonds in the primary structure are not broken, but the polypeptide
chains unravel and lose their specific shape.
· It can be caused by changes in pH, salt concentration or temperature.
Denaturing of a globular protein
Denaturing of a fibrous protein…read more

Slide 7

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A clearly presented PowerPoint on amino acids and proteins which would be useful for any A level biology student needing to study this topic. The slides can be printed off and usefully used as revision cards. 



Really great...thanks alot...provided additional information that my notes didnt have and allowed me to understand the topic fully



nice name ;)

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